There are a large number of different flowlines that are utilized in oil and gas productions systems including, for example, production flowlines to carry hydrocarbon products, hydraulic fluid supply lines, injection fluid flowlines, and so forth. Flowlines that carry fluids from the seafloor to the surface are generally termed risers, while flowlines that carry the production fluid to the shore, across the land, to a transportation device or to a storage facility are termed pipelines or export lines. Risers can include production risers, drilling risers, top tensioned risers, and the like. Other flowlines include jumpers that are shorter segments that connect a subsea well back to its manifold, fluid transfer lines that connect riser systems to floating production units, and export flowlines that connect floating production units to off-loading buoys. Multiple flowlines can be combined to form a bundled line, a piggy-back line, or a pipe-in-pipe, and variations of the basic flowline structures are also useful such as flexible catenary risers and hybrid risers. Flexible flowlines have become more attractive for use in such oil and gas applications as they can have high strength and durability, for instance equivalent to that of rigid steel flowlines, while the flexibility of the systems can better function in the dynamic offshore environments in which they are used.
The formation of flexible flowlines that can successfully function in the challenging environments of oil and gas production systems has proven both difficult and expensive. The flowlines must be able to carry the desired fluids such as the recovered hydrocarbon or the supporting fluids including hydraulic fluids and injection fluids without degradation or failure. While single layer flowlines are used in some applications of offshore oil and gas systems, most flexible flowlines for oil and gas applications will include multiple concentric layers that together provide a variety of properties to the flowline such as strength, barrier properties, chemical resistance properties, anti-wear properties, insulation properties, and the like. For instance, one or more inner layers of a flowline can provide barrier properties, preventing permeation of the fluid carried by the flowline through the wall. This layer can also be resistant to chemical degradation by the fluid carried in the flowline and thermal degradation due to the conditions of utilization, so as to maintain the desirable barrier properties over a long life. In addition to good impermeability, chemical and thermal degradation resistance, and flexibility, the material used to form a barrier layer should also exhibit good impact strength at a wide range of temperatures. These barrier layers have typically be formed from polymeric materials including high density polyethylene (HDPE), polyamides (e.g., PA11 or PA12), or polyvinylidene fluoride (PVDF). While these materials can provide adequate barrier layers in many cases, room for improvement remains.
Polyarylene sulfides are high-performance polymers that may withstand high thermal, chemical, and mechanical stresses. Polyarylene sulfides have often been combined with other polymers to improve characteristics of the product composition. For example, elastomeric impact modifiers have been found beneficial for improvement of the physical properties of a polyarylene sulfide composition.
Unfortunately, elastomeric polymers generally considered useful for impact modification are not compatible with polyarylene sulfides and phase separation has been a problem in forming compositions of the two. Attempts have been made to improve the composition formation, for instance through the utilization of compatibilizers. However, even upon such modifications, compositions including polyarylene sulfides in combination with impact modifying polymers still have failed to provide product performance as desired, particularly in challenging applications such as in forming a flexible flowline for use in oil and gas applications that requires flexibility, impermeability, high heat and chemical degradation resistance as well as high impact resistance.
What are needed in the art are flowlines for use in offshore oil and gas applications that include a polyarylene sulfide composition, for instance as a barrier layer of the flowline.